In most synths there are a few hidden functions that are used for 
repairs.
The keys must be pressed first then turn the synth on after...
D-50: SPACE + DECREMENT : Test mode. You can test all buttons, 
foot switch
and notes (for velocity + pressure) Also 
checks
memory and a card...
" + INCREMENT : Gives credits and ROM version.....
" + WRITE : Tests L.A. Chip. You choose exact test 
by hitting
UPPER(Audio test), LOWER(D/A test??), VAL
(mute) and
LOCAL(exit!).
" + DATA TRANS: Initilize global paramaters such as 
tuning, patch
number for startup etc....
Please note, this will not set the D-50's patches back to factory settings, you'll need to laod them via MIDI, or use the original Roland ROM data card.
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